Yersinia pseudotuberculosis is an enteropathogenic gram negative bacterial species that infects humans and other mammals. There are three species of Yersinia that are pathogenic for humans and other mammals: Y. pseudotuberculosis and Y. enterocolitica are enteric pathogens, and Y. pestis is the causative agent of bubonic plague and is believed to have evolved from Y. pseudotuberculosis less than 20,000 years ago. Y pseudotuberculosis is transmitted through the fecal-oral route, when contaminated food and water are ingested. Colonization requires the expression of one or more of the Yersinia virulence factors encoded in a naturally occurring plasmid, pYV.
The virulence plasmid pYV, found in pathogenic Yersinia strains, encodes about 30 genes that are responsible for encoding the structural, regulatory and secretory components of the type III secretion machinery, and for the effector molecules transported by this machinery called Yops (Yersinia outer proteins; see Hueck, C. J. Microbiol Mol Biol Rev 62: 379-433, 1998 for a review of type III secretion systems). This plasmid-encoded type III secretion system allows Yersinia to secrete and translocate Yops into the host cell where they disrupt cellular processes.
Chromosomal genes encoding a second type III secretion machinery have been found in Yersinia spps. The chromosomally-encoded type III secretion system in Y. pseudotuberculosis is different from the chromosomally-encoded type III secretion system found in Y. enterocolitica. In addition, a flagellar secretion system in Y. enterocolitica, Y. pseudotuberculosis and Y. pestis is a transport system that has homology to type III secretion systems.